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Development of protective coatings to improve high temperature corrosion resistance in chlorine containing environments based on an advanced corrosion risk assessment tool [Elektronische Ressource] / vorgelegt von Hadj Latreche

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170 pages
Development of protective coatings to improve high temperature corrosion resistance in chlorine containing environments based on an advanced corrosion risk assessment tool Von der Fakultät für Georessourcen und Materialtechnik der Rheinisch -Westfälischen Technischen Hochschule Aachen zur Erlangung des akademischen Grades eines Doktors der Ingenieurwissenschaften genehmigte Dissertation vorgelegt von Dipl.-Ing. Hadj Latreche aus Montbéliard Berichter: Prof. Dr.-Ing. M. Schütze Univ.-Prof. Dr.-Ing. W. Bleck Tag der mündlichen Prüfung: 12. März 2009 Diese Dissertation ist auf den Internetseiten der Hochschulbibliothek online verfügbar Acknowledgment This thesis arose at the Karl-Winnacker-Institut der DECHEMA e.V. in Frankfurt am Main was supported financially by the Arbeitsgemeinschaft industrieller Forschungsvereinigungen (AiF) and the German Ministry for Research and Technology, who are gratefully thanked. I would like to express my deep gratitude to Prof.Dr.-Ing. Michael Schütze for his supervision and helpful discussions as well as the careful reading of the present work. I would also like to thank Univ.Prof.Dr.-Ing. Wolfgang Bleck for reviewing this thesis and for his great interest in this work. Technical collaborators of the Karl-Winnacker-Institut have contributed to the production of the present work, and to them I give my hearty thanks. These include, P.
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Development of protective coatings to improve high temperature corrosion
resistance in chlorine containing environments based on an advanced
corrosion risk assessment tool

Von der Fakultät für Georessourcen und Materialtechnik der
Rheinisch -Westfälischen Technischen Hochschule Aachen

zur Erlangung des akademischen Grades eines

Doktors der Ingenieurwissenschaften

genehmigte Dissertation

vorgelegt von
Dipl.-Ing. Hadj Latreche

aus Montbéliard

Berichter: Prof. Dr.-Ing. M. Schütze
Univ.-Prof. Dr.-Ing. W. Bleck

Tag der mündlichen Prüfung: 12. März 2009

Diese Dissertation ist auf den Internetseiten der Hochschulbibliothek online verfügbar






















Acknowledgment

This thesis arose at the Karl-Winnacker-Institut der DECHEMA e.V. in Frankfurt am Main
was supported financially by the Arbeitsgemeinschaft industrieller Forschungsvereinigungen
(AiF) and the German Ministry for Research and Technology, who are gratefully thanked.

I would like to express my deep gratitude to Prof.Dr.-Ing. Michael Schütze for his supervision
and helpful discussions as well as the careful reading of the present work.
I would also like to thank Univ.Prof.Dr.-Ing. Wolfgang Bleck for reviewing this thesis and
for his great interest in this work.

Technical collaborators of the Karl-Winnacker-Institut have contributed to the production of
the present work, and to them I give my hearty thanks. These include, P.Gawenda, M.Schorr,
G.Schmidt, M. Röhrig, S. Gansler, E. Berghof-Hasselbächer, D.Hasenpflug.

In addition, I also thank all other members of the HTW Team for the friendly environment
that they created. My special gratitude goes to Dr. Till Weber and Dr. Patrick Masset for
sharing their experiences.

Finally, a word of thanks should be given to my family, and particularly to my lovable wife
Lili for the encouragements.

Frankfurt, August 2008






Que la séduction sournoise de la connaissance….
Ne me mène aveuglement vers son ennemi qu’est la suffisance…




À mon adorable petite Lili….
À Ceux sans Qui rien ne serait…











Abstract
The presence of chlorine in several areas of chemical industry, as well as in waste incinerators
or plastic/polymer decomposition mills, may significantly reduce the life-time of the plant
components due to its significant corrosivity potential. The development of protective
metallic coatings is one of the solutions that may be taken to promote the long-term resistance
of structural materials involved in these processes. A helpful tool can be corrosion prediction
diagrams for designing optimized coating compositions.
For this reason, a new concept for the assessment of high temperature corrosion resistance in
oxygen-chlorine containing environments has been developed. This development was based
on an evaluation of the state-of-the-art and was leading to the concept of the “dynamic” quasi-
stability diagram. This new type of diagram is based not only on thermodynamic
considerations (as for the diagrams existing so far) but also on the products and reactants flow
through a gas boundary layer formed on the material surface.
“Dynamic” quasi-stability diagrams, which were validated by kinetics investigations of pure
metallic elements, suggest that Ni-Al and Ni-Mo-Al systems should be particularly suitable as
protective coatings. In the present work such coatings were developed and characterized.
After exposure tests under “oxidising” and “reducing” conditions, NiAlMo APS-coatings
offered a higher corrosion protection potential than NiAl APS-coatings under both conditions.
Under "reducing" environments, NiAlMo APS-coatings showed a particularly high corrosion
resistance in comparison with conventional Ni-base and Fe-base alloys investigated in
previous work.

Kurzfassung
Das Vorhandensein von Chlor in mehreren Bereichen der chemischen Industrie sowie in
Müllverbrennungsanlagen oder in Kunststoff-Aufbereitungsanlagen reduziert die
Lebensdauer der Bauteile aufgrund seiner hohen Korrosivität. Die Entwicklung von
metallischen Korrosionschutzschichten ist eine mögliche Lösung, um die
Langzeitbeständigkeit von Strukturwerkstoffen in diesen Anwendungsbereichen zu erhöhen.
Eine wertvolle Hilfe stellt die Entwicklung von Werkstoffbeständigkeitsdiagrammen dar, um
die Auswahl der Beschichtungszusammensetzung der Korrosionsschutzschicht zu optimieren.
Zu diesem Zweck wurde ein neues Konzept zur Beurteilung der
Hochtemperaturkorrosionsbeständigkeit in Sauerstoff-Chlor-Atmosphären entwickelt. Diese
Entwicklung basiert auf der Bewertung des Stands der Technik und führte zum Konzept des
“dynamischen“ Quasi-Stabilitätsdiagramms. Dieses neue Diagrammkonzept beruht nicht wie
die bisherigen Diagramme nur auf der Grundlage thermodynamischer Überlegungen, sondern
berücksichtigt auch den Transport der Reaktanden und der chemischen Reaktionsprodukte
durch eine Gas-Grenzschicht auf der Materialoberfläche.
Die entwickelten “dynamischen“ Quasi-Stabilitätsdiagramme, die durch kinetische
Untersuchungen der reinen metallischen Elemente validiert wurden, deuten darauf hin, dass
insbesondere Ni-Al und Ni-Mo-Al Schutzsysteme als Korrosionsschutzschichten geeignet
sind. Schichten dieser Art wurden in der vorliegenden Arbeit entwickelt und charakterisiert.
Sowohl nach Auslagerung unter "oxidierenden" und als auch unter "reduzierenden"
Bedingungen zeigen NiAlMo APS-Beschichtungen ein höheres Korrosionsschutzpotential als
NiAl APS-Beschichtungen. In "reduzierenden" Umgebungen zeigen NiAlMo APS-
Beschichtungen eine besonders hohe Korrosionsbeständigkeit im Vergleich mit Ni-Basis- und
Fe-Basis-Legierungen, die in einer vorangegangen Arbeit untersucht wurden.















CONTENTS
CONTENTS

1. INTRODUCTION ...............................................................1
2. STATE OF THE ART.........................................................4
2.1 High temperature corrosion..................................................................... 4
2.2 High temperature oxidation 4
2.2.1 Metal-oxygen reaction................................................................................ 4
2.2.2 Growth of oxide scales ............................................................................... 6
2.3 Thermodynamics of high temperature corrosion in chlorine
environments........................................................................................................ 8
2.3.1 Fundamentals.............................................................................................. 8
2.3.2 Different types of diagrams for theoretical corrosion risk prediction 13
2.3.2.1 Conventional stability diagram......................................................................... 13
2.3.2.2 Quasi-stability diagram ..................................................................................... 14
2.3.3 Experimental observations on the stability of pure metals and as
alloying elements ..................................................................................................... 17
2.4 Kinetics of high temperature corrosion in chlorine environments .... 21
2.4.1 Fundamentals............................................................................................ 21
2.4.2 Experimental investigations on the kinetics behaviour of pure metals
and their alloying effects......................................................................................... 26
2.5 Atmospheric Plasma Spraying (APS)-coatings for corrosion
protection ........................................................................................................... 28
2.5.1 Thermal spray techniques ....................................................................... 28
2.5.2 Atmospheric Plasma Spraying (APS)..................................................... 28
2.6 Thermal expansion of solids................................................................... 30 CONTENTS
3. MATERIALS AND EXPERIMENTAL METHODS.....31
3.1 Materials and specimen preparation .................................................... 31
3.1.1 Bulk materials........................................................................................... 31
3.1.2 APS-coatings ............................................................................................. 34
3.2 Test program and experimental methods............................................. 36
3.2.1 Measurement of the coefficients of thermal expansion (CTE)............. 36
3.2.2 Thermogravimetric measurements......................................................... 38
3.2.3 Exposure tests ........................................................................................... 39
3.2.3.1 Bulk materials..................................................................................................... 39
3.2.3.2 APS-coatings....................................................................................................... 41
3.3 Sample analysis after the exposure tests............................................... 41
3.3.1 Metallographic investigation................................................................... 41
3.3.2 Scanning Electron Microscopy (SEM) and Electron Probe
Microanalysis (EPMA) ........................................................................................... 42
4. RESULTS ...........................................................................43
4.1 Microstructural characterisation of the materials and coatings before
exposure.............................................................................................................. 43
4.1.1 Bulk materials........................................................................................... 43
4.1.1.1 NiAl bulk material.............................................................................................. 43
4.1.1.2 Alloy L2 ............................................................................................................... 43
4.1.1.3 Alloy L3 44
4.1.1.4 Alloy L4 45
4.1.2 Coatings..................................................................................................... 46
4.1.2.1 NiAl APS-coatings.............................................................................................. 46
4.1.2.2 NiAlMo APS-coatings ........................................................................................ 49
4.2 Coefficients of thermal expansion (CTE) ............................................. 53
4.2.1 Determination of the heating rate to ensure experimental
reproductibility........................................................................................................ 53 CONTENTS
4.2.2 Coefficients of thermal expansion of NiAl and the NiAlMo bulk
materials................................................................................................................... 54
4.2.3 Comparison of the experimental CTEs with the Bozzolo-Ferrante-
Smith (BFS) model .................................................................................................. 56
4.2.3.1 The Bozzolo-Ferrante-Smith (BFS) method.................................................... 56
4.2.3.2 Results given by the BFS prediction and comparison with experimental
values……………………………………………………………………………………57
4.2.4 Conclusions on the suitability of NiAl and NiAlMo alloys as protective
coating for conventional steels in terms of the CTE ............................................ 62
4.3 Exposure tests of the pure metals and two reference alloys in
chlorine/oxygen environments ......................................................................... 64
4.3.1 Thermogravimetric curves and calculation of the rate constants of
evaporation k ........................................................................................................... 64 l
4.3.1.1 Aluminium .......................................................................................................... 64
4.3.1.2 Molybdenum ....................................................................................................... 66
4.3.1.3 Alloy 201 (nickel)................................................................................................ 67
4.3.1.4 Zirconium............................................................................................................ 68
4.3.1.5 Hafnium............................................................................................................... 69
4.3.1.6 NiAl alloy and alloy B2 ( β-Ni Mo phase): influence of alloying on the kinetics 4
of Ni, Al and Mo chlorination ....................................................................................... 70
4.3.1.7 Summary of the linear evaporation rate constants k calculated from the l
thermogravimetric curves ............................................................................................. 71
4.3.2 Assessment of the activation energies of metal chloride evaporation.73
4.3.3 Preliminary conclusions from the kinetics investigations .................... 74
4.4 Exposure tests of the experimental alloys in chlorine/oxygen
environments...................................................................................................... 75
4.4.1 Short term exposure in “reducing” atmosphere ................................... 75
4.4.1.1 Alloy L2 ............................................................................................................... 75
4.4.1.2 Alloy L3 75
4.4.1.3 Alloy L4 76
4.4.1.4 Conclusions for this atmosphere....................................................................... 78
4.4.2 Short term exposure in “oxidising” atmosphere ................................... 78 CONTENTS
4.4.2.1 Alloy L2 ............................................................................................................... 78
4.4.2.2 Alloy L3 80
4.4.2.3 Alloy L4 80
4.4.2.4 Conclusions for this atmosphere....................................................................... 81
4.4.3 Longer term exposure at 600°C in “reducing” atmosphere: influence
of Mo in the NiAl binary system ............................................................................ 81
4.4.3.1 NiAl...................................................................................................................... 81
4.4.3.2 Alloy L2 ............................................................................................................... 84
4.4.3.3 Alloy L3 84
4.4.3.4 Alloy L4 84
4.4.3.5 Conclusions for longer term exposure.............................................................. 84
4.5 Exposure tests of the APS-coatings ....................................................... 85
4.5.1 Exposure in “reducing” and “oxidising” atmospheres......................... 85
4.5.1.1 Exposure in “reducing” atmosphere ................................................................ 85
4.5.1.2 Conclusions for this atmosphere....................................................................... 88
4.5.1.3 Exposure in “oxidising” atmosphere 89
4.5.1.4 Conclusions for this atmosphere 93
4.5.2 Longer term exposure in “reducing” atmosphere ................................ 94
4.5.3 Conclusions of the longer term exposure in “reducing” atmosphere.. 94
5. DISCUSSION .....................................................................98
5.1 Prediction diagrams................................................................................ 98
5.1.1 Quasi-stability diagrams........................................................................ 100
5.1.1.1 Hertz-Langmuir equation 100
5.1.1.2 Development of quasi-stability diagrams for zirconium and hafnium....... 103
5.1.1.2.1 Quasi-stability diagrams for hafnium ................................................................. 103
5.1.1.2.2 Quasi-stability diagrams for zirconium............................................................... 105
5.1.1.2.3 Comparison of the quasi-stability diagrams of different elements ................... 106
5.1.1.3 Limitation of the quasi-stability diagrams..................................................... 107
5.1.2 Building the basis for a new type of diagram, the “dynamic” quasi-
stability diagram: assessment of corrosion based on transport through the gas
boundary layer....................................................................................................... 109

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